Bleaching



United States Patent "ice 3,156,654 BLEACHING Jan 0. Konecny and RobertE. Meeker, both of Berkeley, Calif., assignors to Shell Gil Company, NewYork, N.Y., a corporation of Delaware No Drawing. Filed June 19, 1961,Ser. No. 117,791 5 Claims. (Cl. 25295) This invention relates to theimprovement of peroxide bleaching, particularly to a method forincreasing the bleaching activity of peroxides and to novel compositionswhich are advantageous for all kinds of bleaching.

A variety of peroxides, including hydrogen peroxide, inorganic persaltssuch as the water soluble perborates, percarbonates, perphosphate etc.,percarboxylic acids and the like have been used for bleaching,especially, textiles. Persalts in particular have been widely used,particularly in Europe, in detergent compositions to provide bleachingsimultaneously with laundering. These compositions have had to be usedat boiling temperatures in order to achieve a satisfactory bleach. Thishas precluded their use in home washing machines since temperaturesabove about 50 to 60 C. are generally not feasible therewith.

A number of proposals have been made for improving the effectiveness ofperoxide bleaching agents. U.S. Patent 2,898,181 recommends the additionof certain amides to washing compositions containing perborate bleachingagents so they can be used at temperatures of about 60-70 C. Specialcarboxylic acid esters are described in British Patent 836,988 as usefulfor improving textile bleaching with either aqueous hydrogen peroxide orinorganic persalts while British Patent 847,702 shows the use of ureafor making percarboxylic acids more useful bleaching agents. GermanPatents 1,010,048 and 1,018,181 disclose the use of formamide andorganic nitriles, respectively, as accelerators of bleaching withperoxides. These additives are not as effective as would be desirableand must be used in relatively large amounts, to 100 mole percent of theperoxy-bleaching compounds, in order to match the bleaching which can beobtained at boiling temperatures with sodium perborate, for example. Asa result, the cost of the product is greatly increased and theusefulness of the final composition for some purposes may be interferedwith by the large amount of additive.

An important object of the present invention is the provision ofbleaching compositions which avoid the foregoing disadvantages of priorperoxy bleaching agents. A particular object is the provision of novelbleaching compositions which contain a new type of accelerator ofperoxide bleaching which has such a high activity that only a relativelysmall amount is suficient to insure the desired effective bleaching.Another object is to provide a new method of textile bleaching withperoxidic com pounds in which improved bleaching can be obtained withoutexcessive peroxide loss through decomposition. A special object is theprovision of detergent compositions which are capable of providingdesirable bleaching action during laundering in home Washing machines.Still other objects and advantages of the invention will be apparentfrom the following description of suitable modes of carrying out theinvention which, however, is not limited to the advantageousmodifications thus given by way of illustration.

It has been discovered that the bleaching activity of peroxy compoundscan be materially improved by using therewith heavy metal ions whichcatalyze peroxide decomposition together with a special type ofchelating agent for said heavy metal. The chelating agent must be onewhich is not only itself stable and without undesirable catalytic effecton peroxide decomposition in the bleaching composition and/or bath inwhich it is to be used,

3,l56,54 Patented Nov. 10, 19 64 but also should be one which forms acomplex with the said heavy metal ions which complex is soluble andsimilarly stable in the bleaching bath. The chelating agent used mustfurthermore be one which is not a stronger complexing agent for theheavy metal ions present than is the material to be bleached. When theheavy metal ion peroxide decomposition catalyst and chelating agenttherefor are selected so they have this unique relationship to thematerial which is to be bleached, they cooperate to accelerate andenhance the bleaching by peroxide bleaching agents making them effectiveat lower temperatures so that their use in home laundry equipmentbecomes practical. This is quite unexpected since heavy metal ions wouldhave been predicted to be undesirable in bleaching with peroxides. Theywould have been expected only to promote loss of peroxide throughdecomposition without providing any advantage. There was no reason topredict any acceleration or improvement in bleaching effect from theaddition of a chelating agent. Indeed many combinations of heavy metalions with chelating agents therefor do not show the advantages of theinvention. Only by proper choice of the heavy metal catalyst of peroxidedecomposition and of chelating agent not only with respect to eachother, but also in regard to the adsorptive power of the material to bebleached relative to complexing strength of the chelating agent can thenew results of the invention be obtained.

With the heavy metal and chelating agent chosen in the above-indicatedspecial relationship to each other and to the material to be bleached,it has been found that there will be a substantial adsorption of heavymetal ions on the material to be bleached but at the same time the heavymetal ions not so adsorbed will be maintained in solution in an inertcomplexed form so they will not catalyze undesirable decomposition ofperoxide. Representing the complexing agent by Q and the material to bebleached as R, one can write equations representing the equilibria whichcontrol the proportion of the heavy metal ions which will be availablefor promoting the desired bleaching and which will be held in inertcomplexed form in the solution so that loss of peroxide throughundesirable decomposition away from contact with the material beingbleached can be minimized. These are,

using cobalt ions as an example of suitable heavy metal ions:

Thus besides its desirable synergistic effect in promoting thebleaching, the chelating agent should also preferably form sufficient ofthe chelate (CoQ) to maintain essentially all the heavy metal ions notadsorbed on R in inert soluble complexed form so that undesirableperoxide decomposition is minimized without interfering with therequired amount of adsorption of cobalt ions indicated in the second ofthese equations.

Thus an important feature of the invention is that it provides a simple,one step method of operation whereby bleaching is improved by heavymetal ions adsorbed on the material to be bleached so as to catalyze thedeco1nposition of the peroxide at the precise location where bleachingis desired. The metal ions are believed to decompose hydrogen peroxideby a catalytic cycle illustrated, in the case of copper ions, by theequations:

This localized production of OH radicals from the peroxide'initiallypresent as the peroxide bleaching agent, either by direct catalyticdecomposition as when using hydrogen peroxide or by catalyticdecomposition of such peroxide formed from the starting peroxidebleaching agent, for instance by hydrolysis of a .peracid or persaltsuch as a perborate or the like. These OH radicals are among thestrongest oxidizing agents known and probably contribute to the observedimprovement in the bleaching. However, that may be, the improvement inbleaching obtained by using the indicated combination of chelating agentand heavy metal ions depends on the amount of heavy metal ion adsorbedon the fabric or other material being bleached, e.g., Co++ adsorbed onR. It has been found that with a constant amount of chelating agent suchas pyridine-Z-carboxylic acid for example, the bleach increases withincreasing amounts of cobalt sulfate or the like. With a constant amountof the latter and increasing amounts of the chelating agent, sufficientin all cases to provide an appreciable excess and thus preventprecipitation of heavy metal hydroxide which would promote undesirableperoxide decomposition, the bleaching decreases, the decrease beingcoincident with decreased adsorption of heavy metal ions by the fabric.The total concentration of heavy metal in the bleach bath can be variedwidely Without detrimentally aifecting'the bleach provided the heavymetal to chelating agent ration is maintained at a proper constantratio.

It is not desirable to use peroxide decomposition catalysts such asheavy metal ions alone. A small improvement in bleaching can indeed beobtained by adding copper or cobalt sulfate to a sodium perboratebleaching bath, for example. But the increase in bleaching effect issmall and accompanied by extensive peroxide loss through decompositionboth by the metal ions and precipitated hydroxides. For example, whenbleaching of a standard cotton test cloth for 15 minutes with sodiumperborate grams per liter of bleach solution) at 60 C., the addition of0.015 millimole of copper sulfate per liter, results in an increase ofreflectance (AR) of the cotton cloth of 9.4 units compared with 6.1units under the same conditions without added copper sulfate, but theloss of peroxide through decomposition is increased from 10% to 32%.However, when the catalysis of peroxide decomposition by copper islocalized at the surface of the cloth, the increase in reflectance (AR)is 17.4 units and the loss of peroxide in the solution not in contactwith the cloth is no greater than when no copper is used.

Any of the heavy metals of the transition series which catalyze thedesired decomposition of peroxide at the surface to be bleached can beused provided the proper chelating agent is employed therewith. Inmaking up liquid or powdered bleaching composition-s it is advantageousto add the heavy metal and chelating agent therefor to the peroxidebleaching agent as a preformed complex of heavy metal with the chelatingagent. Such preformed complexes can also be added to the solution usedfor bleaching separately or together with the peroxide bleaching agent.The preformed complex can be made readily by mixing together in aqueoussolution the chosen chelating agent with a suitable source of therequired metal ions. Alternatively one can add to the peroxide-contain:ing bleaching solution the source of heavy metal ions and chelatingagent separately. In this case it is desirable to introduce thechelating agent first and to then add the heavy metal so that localizedhigh concentrations which can catalyze loss of peroxide by decompositionare avoided. Soluble salts are one of the more convenient sources of therequired heavy metal ions. Inorganic soluble salts are generally moreeconomical but other sources of heavy metal ions can also be usedsuccessfully. Copper and cobalt chlorides, sulfates, nitrates,perchlorates and the like are typical of the salts which are useful.Other metals whose salts can be used in the same Way include chromium,manganese, iron, nickel, zinc, molybdenum, ruthenium, silver, cadmium,tungsten, osmium, gold and ther- -cury. Thebest results are. usuallyobtained, however,

with copper. and cobalt salts. Cobalt salts have. special advantagesbecause of their outstanding effectiveness in improving peroxidebleaching when used with a chelating agent in accordance with theinvention.

The chelating agent chosen should preferably be one which forms achelate complex with the heavy metal or mixture of heavy metal ionswhich chelate is soluble in the bleaching solution to the extent of atleast 5 l0 moles per liter of solution. While there are differences inthe effectiveness of various chelating agents with different heavy metalcatalysts in bleaching different materials, all those which will give upheavy metal to the material being bleached can be successfully used.

There are special advantages in using as the chelating agent aparticular subgroup of amino carboxylic acids having not more than 2carbon atoms separating the 'carboxyl group frorrithe amino nitrogenato'rnj These are the pyridine-2-carboxylic acids such as pyridine-2-carboxylic acid itself and pyridine-2,6-dicarboxylic acid and the like,which meet the foregoing requirements as to complexing power. These arenot only outstanding in their effectiveness as bleach promoters but alsoare especially advantageous in minimizing loss of peroxide byundesirable decomposition during bleaching by the new method. Otheruseful pyridine carboxylic acids are described in US. Patent 2,624,655as useful hydrogen peroxide stabilizer. An es ecially preferred subgroupof these chelating agents are those having a pyridine ring which issubstituted by a single carboxy group attached to the 2-position of thering, as for example, picolinic acid, 4-methyl-picolinic acid, and thelike. The amino carboxylic acids can be used in the free acid form or astheir water soluble salts, particularly the alkali metal salts or thelike.

Another type of aminocarboxylic acid chelating agents which can be usedin bleaching materials which have a stronger adsorption power for heavymetal ions than does cellulose are the compounds which contain at leastone N,N-dicarboxyalkylarnino group, N-(R-COOX) wherein R is an alkyleneradical of up to two carbon atoms and X is hydrogen or a salt-formingcation such, for instance, as an alkali metal or alkaline earth metal orammonium ion, the two indicated Xs being the same or different. US.Patent 2,371,623 describes a number of polycarboxy amines of this kindsuch as nitrilotriacetic acid, aminoethyl-N,N-diacetic acid,ethylenediamine-N,N,

N',N-tetraacetic acid, etc., which can be successfully used in the stocksolutions of the invention. Especially advantageous are thosepolycarboxy amines which contain a plurality of N,N-discarboxyalkylaminogroups in the molecule, especially those having at least two adjacentcarbon atoms to each of which is directly attached at least one of saidN,N-dicarboxyalkylamino group. A particularly suitable sub-group ofpolycarboxyamines of this preferred type are the water-solubleN,N-(dicarboxyalkyl)amino-substituted carbocyclic compounds having asaturated carboeyclic ring with at least two adjacent ring carbon atomseach directly linked to the nitrogen atom V of an N,N-di(carboxyalkyl)amino group containing up to two carbon atoms in each of said alkylradicals. Examples of water-soluble chelating agents of this type arethe 1,2-diaminocycloalkane-N,N,N',N-tetraacetic acids and their saltshaving 5 to 18 carbon atoms in the cycloalkane radical, such as1,Z-diaminocyclopentane-N,N,N', N-tetraacetic acid, disodium1,Z-diaminocyclohexane-N, N,N,N'-tetraacetic acid, tetra-potassium1,2-diaminoperhydronaphthalene-N,N,N,N'-tetraacetic acid, tri-arnmonium4,7-diisobutyl-1,Z-diaminoperhydronaphthalene-N, N,N,N-tetraaceticacidand the like. i e

At least a sufiicientamount of chelating agent for chelating with theheavy metal ion or ions used shouldzbe employed in the bleaching bath tocomplex essentially all heavy metal ionperoxide decomposition catalystnot adsorbed by the material being bleached. More advantageously anexcess of organic-chelating'agent over such amount is used. As a generalrule amounts between.

about 0.01 to about. 20 millimolesof chelating agent per liter ofbleaching solution are employed and most desirably amounts between about0.05 to about 1 millimole per liter. The amounts of heavy metal ion andchelating agent used can be relatively small compared with the amount ofperoxide bleaching agent employed since the action of the complex iscatalytic in the bleaching. Suitable amounts of heavy metal are about0.001 to about 1, more advantageously between about 0.01 and about 0.3millimole per liter of the bleaching solution used. Bleaching solutionscontaining peroxide bleaching agent in concentrations of at least about0.2 millimole per liter and more preferably about 3 to about 140millimoles per liter, are used. In choosing the proportions of thedifferent components to use within these ranges, the relationshippreviously noted in connection with the discussion of the equilibriuminvolved should be kept in mind.

As previously indicated, the invention is applicable with any of theperoxide bleaching agents, such as hydrogen peroxide and per compoundswhich give rise to hydrogen peroxide in aqueous solution. Suitablecompounds include alkali metal persulfates, perborates, percarbonates,perpyrophosphates and persilicates. These are not true persalts in thestrict chemical sense but are believed to contain hydrogen peroxide ofcrystallization, which is liberated in aqueous solution.

The invention can be applied to bleaching baths such as are used fortreating textiles, wood pulp and the like, to wash liquors, such as areused in commercial laundering and to solid bleaching compositions. Solidbleaching compositions prepared according to the invention, preferablycontain the peroxy bleaching agent, source of heavy metal ions andorganic chelating agent therefor in the ratios previously indicated asdesirable in the bleaching bath. In addition, inert salts and any of theconventional adjuncts used in bleaching with or without detergents orother auxiliary agents.

18 carbon atoms per molecule. Examples of non-ionic surface activeagents which can be used in making new bleaching compositions accordingto the invention are the saponines, ethylene oxide condensation productswith fatty acids, alcohols, alkyl phenols, esters, and the like,especially those with alkyl chains of 7 to 14 carbon atoms and 10 to 20glycol units per molecule.

The portions in which the detergents can be used with the new bleachingagents can vary widely. Usually amounts in the range of about 1 to 10parts by weight of detergent or detergent mixture can be used with anamount of peroxide bleaching compound sufiicient to provide about 0.1 to5 parts by weight of active oxygen.

Any of the builders or other additives useful in deter- 15 gents can beused in the new washing compositions of the invention. These includealkaline materials such as alkali metal phosphates, particularly theorthophosphates, tripolyphosphates and pyrophosphates, and silicates, orinert compounds such as alkali metal sulfates or chlorides, or organicadditives of which carboxymethylcellulose and fluorescent agents arerepresentative examples.

The advantages of the invention are shown in the following illustrativeexamples of certain of the Ways in which it can be applied.

Example I A series of bleaching tests were made using a stirred bathcontaining an aqueous solution containing 10 grams per liter of sodiumperborate (NaBO -H O -3H O) as the feet was determined by measuring thereflectance of the sample. The following results were obtained:

Increase in Milllmoles Millimoles Reflectance Peroxide of HeavyComplexing of Cloth* Decom- Heavy Metal Salt Metal M++) Complexiug AgentAgent per (Standard position,

per Liter Liter Units- Percent Maximum: About 20) None None None None 6.1 10 Cobalt sulfate 0. 010 None 7. 6 30 Do 0.020 .do None 8.1 54 Do0.015 Pyridine-2,6-dicarboxylie 0. 25 11. 1 17 act Do 0. 005Pyridine-learboxylic acid 0.25 12.1 17 Do 0.025 o 0.25 15. 7 19*Limiting increase in reflectance under repeated bleaching was 20 units.

When washing and bleaching compositions are prepared by combining anorganic surface active agent with a peroxy bleaching agent, heavy metalsalt and organic chelating agent or a preformed complex of the heavymetal and chelating agent. It is usually desirable to use a largeramount of heavy metal salt because of the tendency of detergents todecrease adsorption of heavy metals by the cloth or other material beingbleached. The organic surface-active agents used can be any of the soapsor synthetic detergents. Alkali metal salts of fatty acids such asstearic and/or palmitic acids, or of rosin acids are examples ofcommonly used soaps which can be employed. Synthetic detergents whichcan be used with or without such soaps include the anionic, cationic andnonionic organic surface-active agents. Typical anionic detergents whichcan be successfuily used in making washing compositions having improvedbleaching action in accordance with the invention include sulfonatessuch as alkyl benzene sulfonates, alkyl sulfonates, sulfonates of fattyacid-monoglycerides, fatty acid oxyethylamide sulfonates,oleylrnethyltauride, sodium alkylphenol polyether sulfonates, and thelike having aliphatic hydrocarbon chains of about 10 to about 20 carbonatoms, and alkyl sulfate salts such as sodium lauryl sulfate, and mixedsecondary alkyl sulfate alkali metal salts of 8 to Example II The effectof adding cobalt sulfate with an excess of pyridine-Z-carboxylic acid,3.10 M cobalt with 2.5.l0- chelating agent, to a bleaching bathcontaining various concentrations sodium perborate was determined in thesame way as in Example I in comparison with bleaching in the same waywithout added catalyst. The following are the results obtained togetherwith the loss of perborate by decomposition in the 1% solution at 15minutes bleaching time.

Example IV Tests to show the amount of heavy metal adsorbed by thecotton cloth in the bleaching were carried out as in Example I using 15minutes bleaching time at 60 C. with a bath containing 10 grams ofsodium perborate per liter to which was added different amounts ofcobalt sulfate and pyridine-Z-carboxylic acid. After bleaching andrinsing the samples of cloth, reflectance measurements were made in theusual way and the amount of cobalt adsorbed was determined by neutronactivation. The following results were obtained:

Cobalt Sulfate Pyridine-2- Cobalt Ad- Bleach (increase added(millicarboxylic acid sorbed on Cloth in reflectance moles per liter)added (millimoles (millimoles per AR units) per liter) 1,000 grams)Example V Cotton cloth was bleached using a stirred vbath containing 10grams per liter of sodium perborate to which had been added 1.1millimoles per liter of sodium pyrophosphate as chelating agent and0.015 millimole per liter of cobalt sulfate. In a 15 minute bleach at 60C., an increase in reflectance of the cloth of 14.7 units was obtained.

xample VI The effectiveness of the new bleaching mixture in combinationwith a commercial, heavily built, alkylbenzene sodium sulfonatedetergent was determined by tests carried out with a mixture of thedetergent Tide with sodium perborate in a Weight ratioof 0.17:1 togetherwith cobalt sulfate and pyridine-Z-carboxylic acid in small amountssufiicient to make their concentrations in the bleaching bath 0.05 and0.25 millimole per liter, respectively. The bleaching was carried out asin Example I using 10 grams of sodium perborate per liter and ableaching time of 15 minutes at 60 C. The bleached cotton cloth showedan increase in reflectance AR of 13.3 units.

While perborate bleaching of cellulose fibers has been emphasized in theforegoing examples, this has been for purposes of simplification of thedescription only and it is to be understood that the invention is notlimited thereto butis broadly applicable to the bleaching of anybleachable material which adsorbs heavy metal ions from aqueous mediausing any peroxide bleaching agent. Among other textile fibers which canbe bleached using .the same operations as with cotton, are the syntheticfibers including polyamide fibers such as Orlon, nylon, Dacron, etc.,polyester fibers of which polyacrylate fibers are an example, etc. Hair,furs, and the like are other types of bleachable materials with whichthe invention can be used.. The bleaching process is also applicablewith cellulose in other forms than fabrics or threads, being useful inpaper pulpbleaching and the like, for instance. ,Witlrthese andsimilanmaterials improved bleaching can be similarly obtained usingother peroxide bleaching agents such as sodium perphosphate or hydrogenperoxide itself for instance.

Still other variations can be made in the invention which will berecognized as not limited to the examples given by way of illustrationnor by any theory proposed in explanation of the improved results whichare obtained.

We claim as our invention:

1. A composition adapted for bleaching cellulosic textiles consistingessentially of granules of sodium perborate uniformly admixed with awater soluble inorganic salt of cobalt, each molecule of said cobaltsalt being in 10 the form of a chelate compound thereof with pyridine-Z-carboxylic acid, there being about 0.2 to about 140 millimoles ofperborate to from about 0.001 to about 1 millimole of Water-solublecobalt salt and 0.01 to 20 millimoles of pyridine-Z-carboxylic acidproviding a molar excess of said acid to water-soluble cobalt saltpresent so that in aqueous solution the chelate gives up cobalt tocellulosic material but preserves the perborate from decomposition bycobalt not absorbed by the cellulosic material.

2. A composition in accordance with claim 1 wherein sodium perborate ispresent in uniform admixture with a chelate of cobalt sulfate andpyridine-Z-carboxylic acid. 3. In a process for bleaching cellulosictextile material by contact with an aqueous solution of a peroxidebleaching agent which gives rise to hydrogen peroxide in aqueoussolution, which bleaching agent is present in a concentration of about0.2 to about 140 millimoles per liter of solution, the improvement ofmaintaining in the solution a concentration of cobalt ion between about0.001 and about 1 millimole per liter of solution, also maintaining inthe solution about 0.01 toabout 20 millimoles of pyridine-Z-carboxylicacid, said pyridine-Z-carboxylic acid being maintained in me- 5 larexcess over the cobalt ions present so that while the cobalt ion isadsorbed on the textile material and catalyzes its bleaching, theremaining cobalt maintaining in the solution a concentration of cobaltions between about 0.001 and about 1 millimole per liter of-solution,also maintaining in the solution about 0.01 to about 20 millimoles ofpyridine-Z-carboxylic acid,

said acid being maintained in molar excess over the amount of cobaltions present so that while cobalt ions are adsorbed from the solution onto the cellulose fibers and catalyze its bleaching, the remainingunadsorbed cobalt ions are maintained in soluble complexed form in thesolution and do not catalyze decomposition of hydrogen peroxide out ofcont-act with the textile material. 5. In a process for bleaching cottoncloth by contact 6 with an aqueous solution of sodium perboratecontaining about 0.2 to about 14.0 millimoles of sodium perborateperliter, the improvement of maintaining in the bleaching solution aconcentration of cobalt ions between about. 0.001 and about 1 millimoleper liter of solution, also maintaining in the solution about 0.01 toabout Y 20 millimoles of pyridine-2-carboxylic acid, the pyridine-Z-carboxylic acid being in molar excess over the cobalt-ionspresent sothat While cobalt ions are adsorbed on the cotton cloth and catalyze itsbleaching, the unadsorbed cobalt ions are maintained in solublecomplexed form which does not catalyze decomposition of the sodiumperborate out of contact with the cloth. 1

(References on followingpage) 9 References Cited in the file of thispatent 3,012,860 UNITED STATES PATENTS $053,634

2,012,462 Agthe et a1. Aug. 27, 1935 2,371,623 Henderson Mar. 20, 1945 5866,764 2,498,343 Rider et a1. Feb. 21, 1950 2,498,344 Rider et a1. Feb.21, 1950 2,624,655 Greenspan Jan. 6, 1953 2,950,175 Johnston Aug. 23,1960 2,961,306 Johnston Nov. 22, 1960 10 2,975,139 Kauffmann et a1 Mar.14, 1961 3,003,910

Dithmar Oct. 10, 1961 10 Meeker et a1 Dec. 12, 1961 Luten et al Sept.11, 1962 FOREIGN PATENTS Great Britain May 3, 1961 OTHER REFERENCESAustin: Principles of Fur Bleaching, Textile Colorist, v01. 65, No. 780,pp. 519-21, December 1943.

Sodium Tripoly Phosphate, Monsanto Technical Bull. No. P439, July 8,1949, Monsanto Chemical Co., St. Louis, Mo., page 3.

1. A COMPOSITION ADAPTED FOR BLEACHING CELLULOSIC TEXTILES CONSISTINGESSENTIALLY OF GRANULES OF SODIUM PERBORATE UNIFORMLY ADMIXED WITH AWATER SOLUBLE INORGANIC SALT OF COBALT, EACH MOLECULE OF SAID COBALTSALT BEING IN THE FORM OF A CHELATE COMPOUND THEREOF WITHPYRIDINE2-CARBOXYLIC ACID, THERE BEING ABOUT 0.2 TO ABOUT 140 MILLIMOLESOF PERBORATE TO FROM ABOUT 0.001 TO ABOUT 1 MILLIMOLE OF WATER-SOLUBLECOBALT SALT AND 0.01 TO 20 MILLIMOLES OF PYRIDINE-2-CARBOXYLIC ACIDPROVIDING A MOLAR EXCESS OF SAID ACID TO WATER-SOLUBLE COBALT SALTPRESENT SO THAT IN AQUEOUS SOLUTION THE CHELAT GIVES UP COBALT TOCELLULOSIC MATERIAL BUT PRESERVES THE PERBORATE FROM DECOMPOSITION BYCOBALT NOT ABSORBED BY THE CELLULOSIC MATERIAL.